The rowing service; Rachel Quarrell's site contains rowing news and hundreds of useful rowing links. The New Rowing Information page has hot up-to-date links to rowing news stories around the world.
David Biddulph's Rowing Pages have a lot of interesting rowing information.
Row2k contains rowing news and links.
RowersWorld is a fund of useful rowing information.
Rowing News is a very good rowing magazine.
For extreme open-water rowing visit the Ocean Rowing Society.
The Sound Rowers Open Water Rowing and Paddling Club
in Puget Sound, Washington State, would appear to be about the most active open-water rowers around, in spite of having no clubhouse or formal center.
The Open Water Rowing Center in Sausalito, California, is a well established, and active, center for open water rowing in San Francisco Bay.
CARA is the UK's 'Coast Amateur Rowing Association', but it only covers the south east.